1. Priority Claim
This application claims the benefit of priority from European Application No. 04010231.1, filed Apr. 29, 2004, which is incorporated herein by reference.
2. Technical Field
The invention is directed to an indoor communication system for a vehicular cabin and to a method for automatically determining an equalizing filter characteristic for an in door communication system of a vehicular cabin.
3. Related Art
A noisy environment may make communication between different people inside a vehicle very difficult, particularly if the noise is as loud as the speech. As a particular example, engine and wind noise may create a loud background noise in a vehicular cabin such as the passenger compartment of a car. The loudspeakers of a car radio and a handsfree telephone system may further interfere with communication between the people in the cabin. As a result of these and other noise sources, communication between passengers in the front seat and the back seat or between the driver and the front seat passenger may be very difficult. Communication may be particularly difficult when the vehicle is moving at a high speed.
In one system, one microphone is associated with each passenger seat, including the driver's seat. The microphone is provided near each seat or near the passenger's head. Each microphone records the speech of the respective passenger and the corresponding signals are output via loudspeakers in the car. Usually, the existing loudspeakers in the car may be associated to the different passenger seats. If a loudspeaker is mounted in each door, each of the loudspeakers may be associated with the person sitting next the respective door. This allows the signals from a particular passenger's speech to be output mainly at the loudspeakers corresponding to the other passengers in the cabin. For example, if the driver is speaking, the corresponding speech signal may be output at all of the loudspeakers except for those near the driver.
This type of indoor communication system, however, has the drawback that, undesirable feedback effects may occur, particularly at higher amplification levels. In principle, this drawback might be overcome by setting the stability limit (i.e., the maximal acceptable amplification) at a very conservative, low level. In other words, the maximal amplification limit may be set to such a low value that under almost all circumstances, no undesired feedback effect will occur. However, this has the undesired consequence that an optimal (higher) amplification, which may be necessary in some cases, will not be achieved. This application describes a communication system for the interior of a vehicle cabin that reduces feedback inside the cabin by automatically determining an equalizing filter characteristic for the communication system.